Hippocampal formation theta activity and movement selection

Hippocampal theta activity results from activation in the ascending synchronizing system. It occurs during sensory/signal processing prior to and coincident with voluntary movements in mammals. The experiments summarized here suggest that it is involved in the organization of motor behaviour. (1) Procaine (a local anaesthetic) infused into the medial septum (MS) abolishes hippocampal theta activity and running behaviour elicited by electrical posterior hypothalamic (PH) stimulation. This indicates that movement elicited by PH stimulation, is dependent on ascending hypothalamo-septal circuitry. (2) Theta can also be recorded in immobile rats prior to the initiation of lateral dodging movements they make in response to conspecific rats attempting to steal their food. Following infusion of atropine into the MS, theta recorded during immobility is abolished and the rats are severely impaired at initiating movements in defence of their food. It is suggested that atropine-sensitive theta is involved in the initiation of movements made by rats in response to sensory stimuli. (3) Rats with fimbria-fornix transections were also less likely to engage in lateral dodging movements in defence of their food, were hyperactive, less thigmotaxic, and defecated more often, compared to control animals. Depth profile analysis of hippocampal field activity in lesioned animals revealed an absence of theta during electrical or chemical pons stimulation. These findings provide evidence that these neural systems are involved in signal processing relevant to movements underlying adaptive behaviour.